He makes some very big assumptions and predications, in other words a strawman argument.
A First Look at ‘Possible artifacts of data biases in the recent global surface warming hiatus’ by Karl et al., Science 4 June 2015Guest Blogger / 3 days ago June 4, 2015
Guest essay by Ross McKitrick University of Guelph
June 4, 2015
Background
The idea that there has been a hiatus in global warming since the late 1990s comes from examination of several different data sets:
Sources: all data accessed through http://www.climate4you.com/GlobalTemperatures.htm except last one, taken from http://www.nature.com/nclimate/journal/v5/n3/full/nclimate2513.html.
The IPCC’s recent report identified this hiatus and commented as follows (Working Group I, Chapter 9, Box 9.2):
The observed global-mean surface temperature (GMST) has shown a much smaller increasing linear trend over the past 15 years than over the past 30 to 60 years… Depending on the observational data set, the GMST trend over 1998–2012 is estimated to be around one-third to one-half of the trend over 1951–2012.
K15 New Estimates
Karl et al. (2015, which I’ll call K15) have struck a very different note, saying that the post-1998 trend is much higher than previously thought, and is in fact about the same as that of the post-1951 interval. Their trend estimate revisions are as follows:
So what changed in the SST records? Bear in mind that there are very few records of air temperatures over the oceans, especially prior to 1950. So to get long term climate estimates, scientists use SST (i.e. water temperature) data, which have been collected since the 1800s by ships. The long term SST records were never collected for climate analysis and they are notoriously difficult to work with. Many judgments need to be made to yield a final record, and as the K15article shows, changes in some of those assumptions yield major changes in the final results.
Read the rest here
http://wattsupwiththat.com/2015/06/04/a-first-look-at-possible-artifacts-of-data...